I only know the spoiler about Hyujae child. IMAGINE THE SHOOOOOCK OM MY FACE WHEN I READ THAT SPOILERRRRER WHATTTTTTTTTT. low-key that's kindaaaaaa weird like you said. But like I guess stuck in a child is better than nothing I suppose, his story was VERY tragic so it's nice he is saved.
My fudanshi goggles are on can you IMAGINE THE PEAK FANFIC
Spoilers
The black dragon used after regression Yoohyun's blood that's why they resemble him but black dragon explicitly said they said no gender they only resemble yoohyun, and its definitely not the pre-regression yoohyun as you said. If you've read around ch 607-8 you'll know that pre regression yoohyun came and killed yoojin in front of current yoohyun on his birthday

Someone spoil me please
What will happen to the OG yoohan? From the original timeline?
You don't have to go into details just tell me if he will remain dead and ice cold alone?